This application is the U.S. national phase of International Application No. PCT/JP99/05605 filed Oct. 12, 1999, which claims priority to Japanese Application No. 10/290194 filed Oct. 13, 1998, each of which is incorporated herein by reference in its entirety.
The retina has a function to receive lights from outside and plays an important role in optic functions. It has a structure consisting of ten layers including the pigment layer of the retina, the inner plexiform layer, the layer of gangliocyte, the layer of nerve fiber and the like to form a tissue with the depth of 0.1-0.5 mm The inner plexiform layer contains neurocyte called amacrine cell which forms synapse in combination with gangliocytic process. This neurocyte is thought to act as a light detector since it shows superior responses at the starting point and the terminating point of irradiation of lights. The layer of gangliocyte contains neurocytes which bodies lie in the inner deepest part of the retina and deeply relates to movement vision, periscope, color perception, form perception and the like. Moreover, the blood vessels of the retina, that are the bifurcated blood vessels originated from the central retinal arteries and veins, run in the layer of nerve fiber and play a role to supply oxygen and nutrient with the optic nerve.
Recently, a notion of so-called xe2x80x9cneuro-protectionxe2x80x9d becomes popular, which says that since in the case of glaucoma, disorders in retina circulation and axonal transport in the retinal nerve ultimately lead to dropping out of nerve fiber caused by death of gangliocytes, promoting the disease to visual field disturbance, developing a way of treatment to prevent or minimize death of gangliocyte will lead to an ultimate treatment of glaucoma (GANKA, 40, 251-273 (1998)). Actually, the papers have been publicized which show that disorders of the layer of retinal gangliocyte and the optic disc were observed even 45 minutes after ischemia in ischemic rats with ocular hypertension (Graefes Arch. Clin. Exp. Ophthalmol., 234, 445-451 (1996)) and that in rabbits with methyl cellulose-triggered ocular hypertension the density of retinal gangliocyte significantly decreased and the density of glia cell significantly increased after the rabbits had suffered from ocular hypertension for 10 days, and that then it was confirmed that there was a correlation between the extend of dropping out of gangliocyte and the size of the cell (Graefes Arch. Clin. Exp. Ophthalmol., 234, S209-S213 (1996)).
When vascular occlusion or hematostenosis occurs in the blood vessels of the retina by an element such as convulsion, clot, embolus, arterial sclerosis and the like, retina circulation is disturbed and supply of oxygen and nutrient to the retina or the optic nerve is blocked. Circulatory disturbance of the retina occupies an especially important position among retinal diseases. Representative examples of the conditions accompanied by circulation disturbance of the retina are retinal vascular occlusion in which the retinal veins or the retinal arteries cause occlusion or stenosis, diabetic retinopathy in which even detachment of the retina likely occurs, and ischemic optic neuropathy in which disorders of optic functions appear. Moreover, due to this circulatory disturbance of the retina, supply of oxygen or nutrient becomes insufficient, leading to death of retinal neurocytes. This death of retinal neurocytes is thought to deeply participate in some hereditary retinal diseases such as macular degeneration, pigmentary retinal dystrophy, Leber""s disease and the like.
And it has been elucidated that apoptosis, that is one form of programmed cell death, shall participate in various forms of thology of eye diseases. For example, the fact that apoptosis occurs in retinal neurocytes is reported in the cases of retinal disorders caused by ischemiaxe2x80x94reperfusion (J. Ocul. Pharmacol. Ther., 11, 253-259 (1995)), detachment of the retina (Arc. Ophthalmol., 113, 880-886 (1995)), retinal degeneration (Proc. Natl. Acad. Sci. USA, 91, 974-978 (1994), Invest. Ophthalmol. Vis. Sci., 35, 2693-2699 (1994)), light-induced retinal degeneration (Invest. Ophthalmol. Vis.
Sci., 37, 775-782 (1996)), glaucoma (Invest. Ophthalmol. Vis. Sci., 36, 774-786 (1995), Exp. Eye Res., 61, 33-44 (1995)) and the like. That is, although there are various causes, it is highly possible that the resulting disorder in optic functions is caused by apoptosis occurring in neurocytes which construct an information network for optic perception.
Then, if there is a drug which has an effect to protect retinal gangliocyte, it is expected to be effective for the treatment of retinal diseases represented by retinal vascular occlusion, diabetic retinopathy, ischemic optic neuropathy, macular degeneration, pigmentary retinal dystrophy, Leber""s disease as well as eye diseases such as glaucoma and the like.
On the other hand, International Patent Application WO 94/02488 discloses K-252a derivatives having a strong effect to promote choline acetyl transferase activity of the spinal cord and being effective for treatments of neurocytic degeneration such as Alzheimer""s disease, amyotrophic lateral sclerosis (ALS), Parkinson""s disease, cerebral ischemia and the like. Moreover, there are also other reports showing that these derivatives suppress apoptosis by the motor neuron (J. Neurosci., 18, 104-111 (1998)) and that these derivatives suppress over-production of tumor necrosis factorxe2x80x94xcex1 and interleukinxe2x80x941xcex2 (in a brochure for International Patent Application WO 97/49406).
However, no report has been publicized which studies these derivatives in ophthalmologic field.
It has been very interesting challenge to find out therapeutic agents for retinal diseases represented by retinal vascular occlusion, diabetic retinopathy, ischemic optic neuropathy, macular degeneration, pigmentary retinal dystrophy, Leber""s disease as well as eye diseases such as glaucoma and the like which have peculiar characteristics in their action mechanisms.
As the inventors put their focus on known drugs used as therapeutic agents for degeneration of neurocyte from the view point of nerve protection and investigated the effects thereof on retinal gangliocyte, it was confirmed that K-252a derivatives protect retinal neurocyte from disorders and it was found that the derivatives are effective as therapeutic agents for retinal diseases represented by retinal vascular occlusion, diabetic retinopathy, ischemic optic neuropathy, macular degeneration, pigmentary retinal dystrophy, Leber""s disease as well as other eye diseases such as glaucoma and the like.
The invention relates to use of K-252a derivatives (it is referred to as the compounds hereinafter) represented by the following general formula (I) for therapeutic agents of optical diseases such as therapeutic agents of glaucoma, therapeutic agents of retinal diseases or the like as well as for remedies of the said diseases.
General Formula (I): 
wherein,
R1 represents a lower alkyl group,
R2 represents a lower alkyl group,
R3 represents a hydrogen atom or a lower alkyl group, and
R4 represents a hydrogen atom or a lower alkyl group
More specifically, according to the invention, medical formulations to treat or prevent eye diseases are provided, which comprise the compound represented by general formula (I) in an amount effective to treat or prevent the eye diseases, as well as vehicles or additives.
As another embodiment of the invention, remedies or preventive methods comprising administering to a patient which needs a remedy or prevention of an eye disease the compound represented by general formula (I) in an amount sufficient to the said remedy or prevention are provided.
As further embodiment of the invention, use of the compound represented by general formula (I) as an active ingredient contained in a medical formulation to treat or prevent an eye disease is provided.
In the context of the invention, the lower alkyl means straight or branched alkyl with 1-6 carbon atom(s) such as methyl ethyl, propyl, butyl, hexyl, isopropyl, isobutyl, tert-butyl or the like.
As a preferable example of the compound, a compound in which both R1 and R2 represent an ethyl group and both R3 and R4 represent a methyl group can be mentioned (it is referred to as Compoud A hereinafter), with the specified structure of the most preferable example represented by the following formula (II). 
Whereas the detailed effects of the compounds on retinal neurocytes will be explained in the section of Pharmacological Tests described hereinafter, it was confirmed that the compounds suppress the decline in the number of the cells in the layer of retinal ganglyocyte when the above-descrived effects were examined using the retina subjected to an ischemiaxe2x80x94reperfusion treatment and the eyes treated with kainic acid.
The route of administration of the compounds can be either parenteral or oral. As dosage forms for parenteral administration, eye drop, injection, nose drop and the like can be mentioned whereas as for oral administration, tablet, capsule, powder and the like can be mentioned, all of which can be formulated using vehicles or additives as well as techniques routinely used in the art. For example, in the case of an eye drop, as the vehicles or additives, isotonizing agents such as sodium chloride, concentrated glycerin and the like, buffering agents such as sodium phosphate, sodium acetate and the like, surfactants such as polyoxyethylene sorbitan mono-oleate (it is referred to as Polysorbate 80 hereinafter), polyoxyl stearate 40, polyoxyethylene hydrogenated castor oil and the like, stabilization agents such as sodium citrate, sodium edetate and the like, as well as preservatives such as benzalkonium chloride, parabens and the like can be used when required to formulate the composition, and pH of the formulation should be within the range acceptable to ophthalmologic formulations with the range of pH 4-8 being preferable.
The dose can be suitably selected depending on the conditions and age of the patient, dosage form and the like, and in the case of eye drops, it is appropriate to administer an eye drop of 0.01-10% (w/v) once or a couple of times a day and in the case of injections, it is usually appropriate to administer 0.0001-1 mg of the compound once a day or in divided doses. Moreover, in the case of oral drugs, it may be usually appropriate to administer 10 xcexcg-1 g of the compound once a day or in divided doses.